Hitherto, a communication apparatus having an interface such as a SONET (Synchronous Optical NETwork)/SDH (Synchronous Digital Hierarchy) interface and an Ethernet (registered trademark) interface are highly standardized, and the commonality of hardware is relatively easy.
A technology has been known that, in a network channel terminating apparatus that terminates SONET/SDH lines with different line speed, processes data on the lines in accordance with clocks corresponding to the line speeds (refer to Japanese Laid-Open Patent Publication No. 2000-69022, for example). Thus, allowing the network channel terminating apparatus to support multiple line speeds can reduce the circuit size, the number of external terminals, the number of man-hours for the development of firmware and the firmware size.
However, clock supply devices and clock interfaces to be used for the synchronization in a SONET/SDH communication apparatus have different specifications among countries. Currently, there coexist standards such as GR standard (telcordia) in North America, ETSI standard in general countries and NTT (registered trademark) standard for communication within Japan, as follows.    (1) North America Specifications: DS1 Interface (speed: 1.544 Mbps, code: AMI/B8ZS and frame: SF/ESF)/1.544 Mbps frame provided by ITU-T G703.704    (2) ETSI Specifications: E1 Interface (speed: 2.048 Mbps, code: HDB3: singleFrame/MultiFrame)/either 2.048 Mbps frame or 2.048 MHz provided by ITU-T G703.704.    (3) NTT Specifications: CREC: 64 K+8 K ITU-T G703.704/CSEND: 6.312 MHz (sin waves)